The present invention is related to a method of transforming an electrical signal representative of a sound wave as a step in the electrical stimulation of a mammalian cochlea or for the purpose of effecting data compression of the electrical signal.
The human cochlea is a complex biochemical-electrical organ of the inner ear that translates sound waves into electrochemical impulses in the auditory nerve. Physically, the human cochlea is a coil having a wound, sound receiving surface, known as the basilar membrane, of approximately 32 mm in length. Over the past twenty years, research in the fields of bioengineering and psychoacoustics have led to enhanced access to the cochleas of hearing impaired individuals and to a better understanding of the critical elements in sound necessary for restoring hearing through the direct electrical stimulation of the cochlea in the hearing impaired. This knowledge has also led to advancement in the compression of sound representation in digital files.
Sound at a particular frequency impinging on the eardrum causes a traveling wave to exist in the cochlea, at the sound frequency with its maximum at a location corresponding to the frequency Sounds with multiple spectral components stimulate different portions of the cochlea, with higher frequency sounds stimulating cochlear loci near the initial (basal) portions of the basilar membrane and lower frequency sounds stimulating the more inner (apical) portions of the coil. Nerve fibers emanating from the various regions of the cochlea are associated with the frequencies that most efficiently stimulate those regions, and the brain, which receives neural impulses from the distributed fibers, maps those frequencies in accord with this association. The nerve stimulated by this traveling wave is associated, in the brain, with the frequency of the sound both due to this mapping of the locus associated with frequency and due to the timing of nerve impulses which tend to reflect the periodicities of lower frequencies. These time patterns of impulses carry information about single frequencies and about the relative magnitudes and phases of multiple frequency components in sounds. For this reason both the spatial mapping of frequencies and the complex timing relationships of the nerve impulses they evoke contribute to the full perception of sounds including speech.
In addition, the relative timing of auditory events at the two ears provides crucial information to a listener. For example, the difference in the times of arrival for sound vibrations at the two ears provides the listener with information about the direction in which the sound has traveled. Until now, the signal processing mechanisms of cochlear implants did not stimulate the cochlea in conformity with the timing of the arriving sound to the point where, even for those patients who were equipped with binaural implants, patients could determine the direction from which sound was arriving.
In addition to hearing restoration, this patent application addresses some problems encountered in the field of data compression of electrical signals representative of sound waves for the purposes-of efficient storage, transmission, and reproduction. One currently popular form of data compression of sound wave signals is included in the xe2x80x9cMotion Picture Experts Group Layer 3 Audio Codingxe2x80x9d or more simply xe2x80x9cMPEG Layer 3.xe2x80x9d Advances in the field of psychoacoustics, specifically an understanding that much of a sound signal is unperceived by a human listener because it is masked by other portions of the sound signal or is redundant because sound energies within a restricted range of frequencies are not distinguished by human hearing, permit MPEG Layer 3 to achieve a data compression ratio of slightly better than ten-to-one. Unfortunately, the creation of an MPEG Layer 3 signal is not a real time process. Because of this, it is not suitable for use in telephony or other real time processes.
The first aspect of the present invention is a method for the real-time transformation of an electrical signal representative of a sound wave that includes the steps of providing an electrical signal representative of a sound wave passing said electrical signal, in parallel, through a number of bandpass filters to create a set of time domain real and imaginary band limited signals. Next, a stream of instantaneous phase angle and magnitude values for each of said set of time domain real and imaginary band limited signals is computed. Thirdly, a stream of electrical pulses or other digital representation of the phase and magnitude information is computed for delivery to a cochlear implant or transmission for decoding and synthesis of the original sound.
In a separate aspect the present invention is a method for effecting hearing restoration by the electrical stimulation of a human cochlea, comprising providing a cochlear implant assembly, including a microphone, a signal processing assembly connected to the microphone and a set of electrodes contacting the cochlea and being operatively connected to the signal processing assembly. Also, the microphone receives sound waves and translates them into an electrical signal and the signal processing assembly detects predefined events in the electrical signal in each frequency band out of a set of frequency bands and emits a set of signals in response to each detection of a predefined event. Additionally, at least one of the set of electrodes electrically stimulates the cochlea in response to each set of signals.
In a further separate aspect the present invention is a method for effecting hearing restoration by the electrical stimulation of the cochlea of a human, comprising providing a cochlear implant assembly, including a microphone, a signal processing assembly connected to the microphone, a set of electrodes contacting the cochlea and being operatively connected to the signal processing assembly. Also, the microphone receives sound waves and translates them into an electrical signal and the signal processing assembly iteratively chooses a frequency-magnitude pair in each frequency band out of a predefined set of frequency bands, each frequency-magnitude pair being representative of the sound in the frequency band. Additionally, the electrodes are stimulated in response to the frequency magnitude pairs.
In a yet further separate aspect the present invention is a method for effecting hearing restoration by the electrical stimulation of a human cochlea, comprising providing a cochlear implant assembly, including a microphone a signal processing assembly connected to the microphone and a set of electrodes contacting the cochlea and being operatively connected to the signal processing assembly. The microphone and the signal processing assembly form a set of abstracted frequency-magnitude pairs based on a sound signal received by the microphone A plurality of the electrodes cooperatively simulate the sound of all magnitude-frequency pairs.
In a still further separate aspect the present invention is a method for the real time data compression of an auditory signal, comprising the steps of converting the auditory signal into a digital electronic signal having an initial sampling rate, in real time and forming a time sequence of abstracted parameter values, representative of the auditory signal, in real time. Additionally, the time sequence is encoded to form an encoded time sequence that includes a full representation of the abstracted parameter values less often than the initial sampling rate of the auditory signal.
The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.